dissolved oxygen processing & qc for biogeochemical-argo · storage drift is always negative...

Dissolved Oxygen Processing & QC for Biogeochemical-Argo

Henry Bittig (IOW), Ken Johnson (MBARI), et al.

BGC-Argo meeting, 19th ADMT, Scripps 04-05 Dec. 2018

What‘s new?− Optode summary paper published in Front. Mar. Sci.− Found their way into Argo O2 documentation

Outline

(1) Review of Processing

(2) RT and DMQC

(3) Open questions

Optode ‘Calibration Zoo’ There are different ways to characterize the Optode O2–T response. And there have been many variants how to do it historically…!− Cookbook “Aanderaa polynomial std. calibration” = batch-foil cal. v1− Cookbook “Aanderaa polynomial std. calibration followed by a two-point

adjustment” = batch-foil cal. v2− Cookbook “Stern-Volmer equation” = foil multi-point calibration

Optode ‘Calibration Zoo’ There are different ways to characterize the Optode O2–T response. And there have been many variants how to do it historically…!− Cookbook “Aanderaa polynomial std. calibration” = batch-foil cal. v1− Cookbook “Aanderaa polynomial std. calibration followed by a two-point

adjustment” = batch-foil cal. v2− Cookbook “Stern-Volmer equation” = foil multi-point calibration

They all come with a different uncertainty – different from what the spec sheet says (“8 µM or 5 %, whatever is greater”).

Assessed by reproducing historic approaches using multi-point calibration data.

Optode ‘Calibration Zoo’ batch-foil cal. v1 vs. multi-point data

after Bittig et al. 2018, Oxygen Optode Sensors: Principle, Characterization, Calibration, and Application in the Ocean, Front. Mar. Sci. 4:429

Optode ‘Calibration Zoo’ ~batch-foil cal. v2 vs. multi-point data

after Bittig et al. 2018, Oxygen Optode Sensors: Principle, Characterization, Calibration, and Application in the Ocean, Front. Mar. Sci. 4:429

Optode ‘Calibration Zoo’ → Better handle on what's the PARAMETER_ACCURACY

(= “plug & play” accuracy when using an O2 optode)

→ See processing cookbook cases, e.g.,

Optode Pressure ResponseReminder: Two-fold pressure response(a) On O2 quenching(b) On luminophore (→ always, even at 0 % O2)

Uncertainty of ~0.3 % per 1000 dbar due to variability between sensors

Bittig et al. 2015, Pressure response of Aanderaa and Sea-Bird oxygen optodes, J. Atmos. Oceanic Techn., 32:2305-2317

reduced quenching

reduced Λ0

Optode Pressure ResponsePotentially changing with time at high pressures?

O2

sat.

Wilken-Jon von Appen (AWI), pers. comm. (2018)

SBE63 on MicroCAT

AADI Optode 4330 2635 m

4571 m

O2

conc

.

0

80

7050

0

50

Uchida et al. (2018), Argo Science Workshop, Japan

O2

sat.

Brian King, pers. comm. (2017)

Optode Pressure ResponsePotentially changing with time at high pressures?

This floats stayed during 5 months in a very small areaApparent drift of about 4 μmol/kg over 5 months

(Slide from Virginie Thierry)

Drift of the optode sensor ?Deep Arvor floats deployed in 2012

Change in deep O2 (believed to be stable)

Hard to distinguish change in O2 response from change in P response...

O2 Quantity ConversionsTypo discovered in B2 exponent. Effect is very small and does not require a complete BGC-Argo DOXY fleet reprocessing. (Objections?)

O2 Quantity ConversionsTypo discovered in B2 exponent. Effect is very small and does not require a complete BGC-Argo DOXY fleet reprocessing. (Objections?)

µmol kg-1

O2 Solubility

Outline


(2) RT and DMQC

(3) Open questions

Why RT and DM Adjustment?

O2 Optodes do drift! (‘Storage’ drift)− affects O2 sensitivity → factor on (p)O2 for correction

Sensors are out of (manufacturer) calibration when deployed and need some way of adjustment. Storage drift is always negative (loss in O2 sensitivity). → Systematic bias in network!→ Proposed ('crude') O2 RT adjustment based on surface climatology to remove

bias, if no other means available (DM, using in-air obs.!).

Bittig et al. 2018, Oxygen Optode Sensors: Principle, Characterization, Calibration, and Application in the Ocean, Front. Mar. Sci. 4:429

RT O2 Adjustment

− ds

RT O2 Adjustment – crude version (3.2.2)

− ds

DM O2 AdjustmentMuch better handle on O2 storage drift!

→ How to build incentives to do DMQC & feed back???

Do and use in-air measurements throughout life of float!

On floats: Established, becoming standard best practice.On gliders: Proven, but rare?

Bittig and Körtzinger (2015), Johnson et al. (2015), Bushinsky et al. (2016), SCOR WG 142 (2015)

In-air Measurements for DM CalibrationCalibration Reference + Additional info about sensor in-situ performance.3 Effects:(1) In-water O2 affects near-surface 'in-air' data ('carry-over').(2) Temperature-compensation for some optodes is inaccurate.

(esp. batch-calibrated)(3) Some sensors drift in-situ, too.

(but less strong than storage drift, and unclear whether all negative)

Bittig et al. 2018, Oxygen Optode Sensors: Principle, Characterization, Calibration, and Application in the Ocean, Front. Mar. Sci. 4:429

In-air Measurements for DM CalibrationCalibration Reference + Additional info about sensor in-situ performance3 Effects:(1) In-water O2 affects near-surface 'in-air' data ('carry-over').

100 % air

100 % waterfloat

O2 slope mi w/o carry-over correction

O2 slope mi with carry-over correction

In-air Measurements for DM CalibrationCalibration Reference + Additional info about sensor in-situ performance3 Effects:(1) In-water O2 affects near-surface 'in-air' data ('carry-over').(2) Temperature-compensation for some Optodes is inaccurate.

(esp. batch-calibrated)

O2 slope mi = const.


(esp. batch-calibrated)

O2 slope mi = const. + a * TEMP


(esp. batch-calibrated)(3) Some sensors drift in-situ, too.

(but less strong than storage drift, and unclear whether all negative)

O2 slope mi = const. + d * time

Storage of in-air measurements in BRtrajAt the 18th ADMT, a decision was reached to abolish MC=1100, and move the assignment of surface data in the Btraj files back to the “true” MCs in the following manner:

• X–10 = in-water samples, part of end of profile, shallower than nominal 10 dbar

• X+10 = in-water samples, part of surface sequence (guidance in RT: before air-bladder inflation / before max. buoyancy)

• X+11 = in-air samples, part of surface sequence (guidance in RT: after air-bladder inflation / after max. buoyancy)

• X–1 = individual surface observations

Data to include should all be in PPOX_DOXY.The X + 10 / X + 11 codes apply only for X = 600 (AET), 700 (TST) and 800 (TET), i.e., when the float is at the surface.Users should be warned that the distinction between X-10, X+10, X+11 is known definitively for some floats (e.g. some newer Apf9i APEX with Optode), but is only a best guess estimate for other floats (e.g. PROVORs).

Uncertainty estimate for in-air DM Calibration+ Uncertainty of in-air correction / O2 slope factor m

+ Uncertainty of base O2 – T calibration (at other O2)

Valid at ~100 % O2 sat. only!

Uncertainty estimate for in-air DM Calibration+ Uncertainty of in-air correction / O2 slope factor m+ Uncertainty of base O2 – T calibration (at other O2)+ Uncertainty of pressure effect (at other pressures)

Bittig et al. 2018.Front. Mar. Sci. 4:429

in hPa (pO2)

Uncertainty estimate for in-air DM Calibration+ Uncertainty of in-air correction / O2 slope factor m+ Uncertainty of base O2 – T calibration (at other O2)+ Uncertainty of pressure effect (at other pressures)

Uncertainty estimate for in-air DM Calibration

Why not apply a constant factor for DOXY_ERROR?


Why not apply a constant factor for DOXY_ERROR?O2 ‘storage’ drift is factor in DOXY, right.


Why not apply a constant factor for DOXY_ERROR?O2 ‘storage’ drift is factor in DOXY, right. – Error is ~constant value at all O2’s!!

Uncertainty estimate for in-air DM Calibrationfdsfsd

Further DMQC guidance

...

Outline


(2) RT and DMQC

(3) Open questions

dissolved oxygen processing & qc for biogeochemical-argo · storage drift is always negative...

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